Distance measuring apparatus



Filed July 51, 1942 2 Sheets-Sheet 2 w W E RmG lbw WW0 m 8 R 6.8 do? R wg. 33 1 Q1 m1 g #\L\ B R 6318 hukmaowmu .NSUMG 30 h mxmg 1 E0233 wiwkfi409200 Q\\ Q mqbklqkm Patented June 10, 1947 DISTANCE MEASURINGAPPARATUS Irving Wolff, Haddoniield, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application J lily 31,1942, Serial No. 452,990

Claims. 1

My invention relates to distance measuring apparatus and particularly tosystems of the type wherein the propagation time of a frequencymodulated radio wave is utilized for determining the distance to areflecting object.

Systems of this general type are described in Bentley Patent 2,011,392and in Espenschied Patent 2,045,071,'for example. In such systemsdistance, such as altitude, is determined by radiating a frequencymodulated wave to the earth or other reflecting object and receiving thereflected wave in a heterodyne receiver located in the vicinity of thetransmitter. The heterodyning or mixing signal for the receiver isobtained directly from the transmitter whereby the receiver outputincludes a signal of difference frequency" which frequency is determinedby the time required for the radiated signal to reach the reflectingobject and return to the receiver.

An object of the present invention is to provide an improved system ofthe above-described type.

A further object of the invention is to provide an improved system ofthe above-described type that will indicate substantially simultaneouslythe distances of a plurality of reflecting objects.

A further object of the invention is to provide an improved means forand method of determin ing distance.

In one preferred embodiment of the invention the output signal of theheterodyne receiver is applied to a sharply tuned circuit such as atuned amplifier which has its output circuit connected to a distanceindicating means. The indicating means may comprise an element carryingan index aperture movable relative to a scale and behind which a lamplights up when signal is passed by the tuned amplifier. Either the indexaperture or the scale is moved in a definite time relation with respectto either a frequency control or an amplitude control of the frequencymodulating wave whereby the rate of frequency sweep (i. e., rate offrequency deviation) of the radiated and reflected signal is diiferentat each position of the index aperture. In this way, over the desiredrange of distances the beat frequency output of the receiver is broughtperiodically to the particular frequency passed by the tuned amplifierand the indicator lamp lights up when opposite the correct distancereading on the scale.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Figures 1, 2and 3 are diagrams showing different embodiments of the invention. Likeparts in the several figures are indicated by similar referencecharacters.

Fig. 1 shows my invention as applied to a system utilizing a rotatinglamp type distance indicator. A transmitter oscillator 10 radiates afreq ency modulated signal from a dipole I This signal, afterreflection, is picked up by a dipole I2 and supplied to a heterodynereceiver l3 which is also supplied over a conductor 14 with thefrequency modulated signal directly from the transmitter ID. Theresulting heterodyne or difference frequency is proportional to thelength of the path ofthe reflected signal times the modulation frequencytimes the amount of frequency sweep or frequency deviation. Stateddifferently, the difference frequency is proportional to the length ofsaid path times the rate of frequency deviation of the signal. Thisheterodyne signal is applied to a sharply tuned amplifier l5 which hasits output circuit connected to a'suitable indicator IT.

The frequency modulation of oscillator [0 may I be accomplished by meansof a sawtooth wave, for

- scribed in detail.

example, supplied from a circuit l8 to a frequency modulator I9. Themodulator 19 may be some means, such as a reactance tube, for varyingthe capacity of a tuned circuit in the oscillator 10. The sawtooth wavecircuit [8 has periodically recurring voltage pulses applied theretofrom a suitable pulse generator such as a blocking oscillator 2i. Thecircuits for the units 18, i9 and 2| are well known in the art and neednot be. de-

As an example of circuits for units I 8 and 2|, reference is made toTolson ct a1. Patent 2,101,520, v

As previously indicated, either the peak amplitude or the frequency(rate ofrecurrence) of the modulating signal may be varied as the indexmark of the indicator I1 is moved. In Fig. 1 it is the frequency of .themodulating wave that is varied. This may be done, for example, by vary-.ing the grid leak resistance of blocking oscillator by means of a motor22 which drives a rotatable potentiometer arm 23 along a potentiometerresistor 24. The portion of resistor 24 that is between the contactpoint of arm 23 and one end of the resistor 24 is in parallel with agrid leak resistor 26 whereby the total grid leak resistance is variedto vary the blocking oscillator frequency as the arm 23 rotates.

synchronously with the rotation of potentiometer arm 23, the arm 21 ofthe indicator I1 is retated by the motor 22. The indicator arm 21 has aneon lamp or the like mounted thereon behind a transparent ortranslucent member carrying scale markings 28. To obtain a sharp indexmark, a mask 29 having a slit aperture 3| therein may be mounted on thearm 21 in front of the neon lamp.

It will be evident that with generator l8 supplying sawtooth waves of aparticular peak amplitude, the "difference frequency" output of receiveri3 is proportional to the length of the path of the reflected wave timesthe rate of recurrence of the sawtooth modulating wave. In other words,for a given altitude or other distance, and

for a given frequency of sawtooth wave of a given peak amplitude, thereceiver output has some definite frequency; such as 50,000 cycles persecond, for example. Assuming, by way of example, that the amplifier I6is tuned to pass signal only at 60,000 cycles, it will be apparent thatfor the example just assumed no sig-nfil d6uId='1assthe amplifier I6 andthe neon lamp would not light. However, the neon lamii li'ght as soon asthe rotation of the potent'idfiit'iirni 13 changes the rate ofrecurrence of the sawtooth wave to a value which makes th receiver eueumave a frequency of 60,000 cycles for the given distance to thereflecting object. Meanwhllej'th lamp and the aperture'offjindex mark 3|have heen "'n'ihvefd along thescale 28 to al'point wlier-"the comerdistance1slliaicdtew-wneni-tiloce cycle vs a preterm-s1 wnue' jenemy-imagines or aeiliatdi m 15 mom ly produce two separate index marksif the relative speed of the airplane and the object is high ihn'ough.-'-'I'hisfact may be taken advantage of to determine at leastapproximately the ground "s'peed of the airplane. Ili'Fig.'3 theinvention is shown with a cath- Ode ray'tube indicator 5|. In theexample assu'iiied, "a sawtooth wave 52 is utilized for frequencymodulation and its peak amplitude is varied by the motor 22synchronously with vari- 5 ations in the maximum amplitude of thevertical jieflec'tion or time axis sweep of the cathode ray.

The cathode ray-tube 51 is o: conventionalconjjfs'truction' nd includesafpai'r or deflecting plates 53an d 53a to which ix-deflecting voltage54 is applied. The-end of tulle 5|" carries-the usual F fluorescentscreen- ('not 's hown-)' and isprovided with a' distance scale 66. Thesawtdoth'wav 54 i's pram-bed by rotation bf an arm 5'Iwhlich m'dves-.'ol,--tap"al0ng' a potentiometer sensor 585 The-arm 51 is mechanicallycoupled to th motdr :2 so

by the arri pllilildi-z or the veftical defldfiion. This action issimilar" to that of the previous1y=aescribed" circuits. I

It is asaimeathat the Cathode ray tubeis biased netic deflecting coil51.

- '-I claim as'myinvention:

1. The method of measuring distance wl'iich comprises radiating a radiowave tbwarda reflecting object, "cyclically frequency iiibduiating saidwave to cau's'e' its frequency to h'ahge 'cycli- EO' -Wherebya signalhai'ing 'afbea't oridifiernbefre- -'quency is produced,periodicallyvaryingthe'rate of said frequency change-'andsyn'chrdnous'lyvary- '-ing the'position 01'' an index marking means' with respect to adi'stance" 'scalef and producing an 55 "indication at said indexni'arlr'ir'ig" means only in response to the'freqiiency of said signalreaching a predetermined heat frequency-value.

2. Th lne'thod Of measuring distalmi' which comprises radiating a"radio' wave 'tbw'ard 'a' re- 00 fleeting object, cyclically modulating"said"='wave tccause itsirequ'ency to change cyc1ically"andsubstantially linearly with respecb to "time; re- =2 civing the waveafter-reflection from-said object and hetero'ciynin'g'itwitli apoi'tionof 'said"i1iodu e5 lat'e'd wave which has riot h'een reflected wherebyto 'a-s'cale; and causin 'sal'd index ma'rking rneans to produce anindication only in response to the frequehibf said Signallddhihhbfedetfinimid beat fi-e'quency value.

3. Incombiination,"a radio-transmitterhnd a receiver located intheieg'ion of said transmitter,

an indicator comprising a scale means for p d n a periodic mo ulatingwave means for cyclically modulating said transmitter by said wave to cnge its frequency in a predetermined way with respect to time, means forheterodyning in said receiver said frequency modulated radio wave afterreflection from an object with said frequency modulated radio wavereceived directly from said transmitter whereby a signal havingaidiflerence fr q ncy i p fl and a relatively movable index markingmeans, a circuit tuned to pass signal of a, certain frequency only andconnected to supply signal from said receiver to said indicator toproduce an index indication in response to passage of signal of saidcertain frequency, and means for cyclically changing the position ofsaid index marking means with respect to said scale and forsynchronously varying said rate of change in the frequency of thetransmitted wave whereby the distance from said transmitter to saidobject may be determined from the position of said index indication withrespect to the scale.

4. In combination, a radio transmitter and a receiver located in theregion of said transmitter, means for producing a periodic modulatingwave, means for cyclically modulating said trans mitter by said wave tochange its frequency substantially linearly with respect to time, meansfor heterodyning in said receiver said frequency modulated radio waveafter reflection from an object with said frequency modulated radio wavereceived directly from said transmitter whereby a signal having adifierence frequency is produced, an indicator comprising a scale and arelatively movable index marking means, a circuit tuned to pass signalof a certain frequency only and connected to supply signal from saidreceiver to said indicator to produce an index indication in response topassage of signal of said certain frequency, and means for cyclicallychanging the position of said index marking means with respect to saidscale and for synchronously vary said rate of change in the frequency ofthe transmitted wave whereby the distance from said transmitter to saidobject may be determined from the position of said index indication withrespect to the scale.

5. In combination, a radio transmitter and a receiver located in theregion of said transmitter, means for producing a periodic modulatingwave, means for cyclically modulating said transmitter by said wave tochange its frequency in a, predetermined way with respect to time, meansfor heterodyning in said receiver said frequency modulated radio waveafter reflection from an object with said frequency modulated radio wavereceived directly from said transmitter whereby a signal having adifference frequency is produced, an indicator comprising a scale and arelatively movable index marking means, a circuit tuned to pass signalof a certain frequency only and connected to supply signal from saidreceiver to said indicator to produce an index indication in response topassage of signal of said certain frequency, and means for cyclicallychanging the position of said index marking means with respect to saidscale and for synchronously varying the amplitude of the modulating wavewhereby the distance from said transmitter to said object may bedetermined from the position of said index indication with respect tothe scale.

6. In combination, a radio transmitter and a receiver located in theregion of said transmitter, means for producing a periodic modulatingwave,

means for cyc ically modu atin saidtransmitter by said wave to changeits frequency in a predee termined way with respect to time, means forheterodyning in said receiver said frequency modulated radio wave afterreflection from an object with said frequency modulated radio wavereceived directly from said transmitter wherebya signal having adiiference frequency is produced, an indicator comprising a scale and arelatively movable index marking means, a circuit tuned to pass signalof a certain frequency only and connected to supply signal from saidreceiver to said indicator to produce an index indication in response topassage of signal of said certain frequency, and means for cyclicallychanging the position of said index marking means with respect to saidscale and for synchronously varying the frequency of the modulating wavewhereby the distance from said transmitter to said object may bedetermined from the position of said index indication with respect tothe scale.

7. In combination, a radio transmitter and a receiver located in theregion of said transmitter, means for producing a periodic modulatingwave, means for cyclically modulating said transmitter by said wave tochange its frequency in a predetermined way with respect to time, meansfor heterodyning in said receiver said frequency modulated radio waveafter reflection from an object with said frequency modulated radio wavereceived directly from said transmitter whereby a signal having adifierence frequency is produced, an indicator comprising a scale and arelatively movable index marking means, a circuit tuned to pass signalof a cer tain frequency only and connected to suppl: signal from saidreceiver to said indicator ti produce an index indication in response topas sage of signal of said certain frequency, ant means for cyclicallychanging the position said index marking means with respect to sai scaleand for synchronously varying both th amplitude and the frequency of themodulatin wave whereby the distance from said transmit ter to saidobject may be determined from th position of said index indication withrespect 1 the scale.

8. In apparatus for determining distance, radio transmitter and areceiver located in tl region of said transmitter, means for produclr aperiodic modulating wave that can be varie in amplitude and infrequency, means for fr quency modulating said transmitter by said waxmeans for heterodyning in said receiver sa frequency modulated radiowave after reflecti' from an object with said frequency modulat radiowave received directly from said trar mitter whereby a signal having adifference f1 quency is produced, an indicator comprising scale and arelatively movable index marki means, a sharply tuned circuit connectedto sr ply signal from said receiver to said indicat and means forrepeatedly changing the positi of said index marking means with respectsaid scale and for synchronously varying at le one of said two variablecharacteristics of modulating wave whereby the distance from stransmitter to said object is shown by the p( tion of said index markwith respect to the sc 9. The invention according to claim 8 who: saidmodulating wave is triangular in wave sh whereby the index mark isspread by the Dow efiect to indicate the speed of said apparatus vrespect to said reflecting object.

10. In combination, a radio transmitter 7 a receiver located in theregion of said transto pass signal or a certain frequency only andmitter, means for producing a periodically recurconnected to supplysignal from said receiver to ring modulating wave, means for cyclicallymodsaid indicator to light said lamp In response to ter whereby a signalhaving a dlfierence fre- 10 said object may be determined from theposition

